During a close flyby, the Cassini spacecraft yielded a new estimate of the mass of Enceladus of 1.08 × 1020 kg. Given that Enceladus’s diameter is 499 km, calculate its density. The larger satellite Tethys has a density of about 1.0 kg/L. What does this density suggest about Enceladus’s composition and geological history relative to Tethys’s?

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Assume Enceladus is a sphere.

V = 4/3πR3 = 4/3π(499 km/2)3 = 6.5 × 107 km3 = 6.5 × 1016 m3

D = M/V = (1.08 × 1020 kg) / (6.5 ×
1019 L) = 1.66 kg/L.

Density of 1.66 kg/l. This gives Enceladus a considerably higher
density than Tethys, indicating that in addition to icy materials,
it must have some silicates and possibly even some iron. Enceladus’
apparent composition (rock and/or iron) may result in some internal
heat in the form of radioactive decay. This could provide the
energy for some of the surface features including smooth terrain
that apparently has been (relatively) recently renewed.